Sound amplifier



C. H. DUFFY SOUND AMPLIFIER Jan. 13, 1931.

Filed April 8, 1929 //v://v To CHAAPL E 8 Has 0 urp/ Arr-o NE) horizontal cross member 6 which connects the two vertical supports 6 provides the mounting for the actuating motor 5, and stiffens the structure.

A suitable connecting clip 11 is employed to connect the diaphragm with the driving pin 12 of the actuating motor 5.

While the driving pin 12 of the actuating unit 5 lies tangential to the meeting edges 2 of the diaphragm 1 at the exterior angles A thereof, as will appear from the cross section illustrated in Figure 3, I prefer to connect the said driving pin 12 to the diaphragm 1 at the point or apex of the interior angle B, at which point the driving pin 12 does not lie tangentially to the meeting edges 2 of the diaphragm, as will appear from Figure 1, which shows a cross section through the diaphragm on a line with said interior angle 13. By this construction, when the diaphragm is flexed into its modified cylindrical formation, it is retained in such formation at three points along the meeting edges 2 of the diaphragm. These three points are located'at the interior angle B and at the juncture of the sheets of the diaphragm at their upper and lower edges. These three points resist the natural tendency of the flexed diaphragm toassume a simple cylindrical formation. Therefore, the greatest tension on the diaphragm is on the line of the interior angle B and on the lines of the upper and lower edges of the diaphragm, while areas of less tension exist on the lines of the exterior angles A. I therefore prefer to connect the driving pin at the interior angle B which is. at the central area of the greatest tension on the diaphragm so that the impulses from the actuating motor are imparted to the diaphragm at this central area of greatest tension to cause the diaphragm to respond more perfectly to the impulses imparted to it through the driving pin. lVhile this shaping of the meeting edges 2 as shown in Fig. 6, produces a very satisfactory diaphragm, the same may be otherwise shaped so that the point of connection with the driving pin may be tangential to the two curves formed by the diaphragm.

lVith particular reference now to Figures 7 and 8, it will be seen that between the forward meeting .edges 2 of the diaphragm, 1 interpose a layer 20 of sound damping material such as felt or the like, and prefer to stitch .or otherwise secure, the said edges and felt together so that the two sections forming the diaphragm are incapable of touching each other and thus create a rattle when the diaphragm is in a state of vibration.

When a diaphragm is made of two pieces of material which are connected together at their meeting edges, there is a tendency for the portions of the diaphragm at the meeting edges to strike against each other and produce a rattle which ruins the reproduction. This is because when in operation both sections of the diaphragm are vibrating, and when'the amplitude of the vibrations are sufficient to cause the meeting edge portions to strike each other, a rattling results.

In order to overcome this disadvantage the meeting edges of the diaphragm sections are spaced apart and preferably a soft material such as a layer of felt or the like is interposed as shown in Fig. 7 This insures that the two sections of the diaphragm vibrate independently in the sense that the vibrations of one section are not imparted to the other section and no rattling results. I

It is likewise to be seen fromFigure 8 that at the top and bottom edges of the diaphragm, I prefer to encase a strip 30 of sound damping material such aselastic webbing, felt or the like and to stitch, or otherwise secure, the same in position as shown. An additional purpose served by this latter construction is to stiffen the edges of the diaphragm. The result is a complete damping out of any rattling at the edges of the diaphragm and a more perfect reproduction of low frequencies which usually create the harsh and unpleasing rattling in speakers of usual design and construction.

I claim:

1. A device for reproducing sound including a modified cylindrical diaphragm having two front meeting edges, means for supporting the diaphragm, means for actuating the diaphragm, connecting means between the actuating means and the two front meeting edges of the diaphragm, and a layer of suitable sound damping material disposed between the two front meeting edges of the diaphragm to prevent the meeting edge portions of the diaphragm from striking each other zvhen the diaphragm is in a state of vibraion.

2. A device for reproducing sound including a curved diaphragm having two front meeting edges, means connected to the two front meeting edges of the diaphragm for actuating the same, and means for damping the vibrations at the two front meeting edges of the diaphragm to prevent the meeting edge portions of the diaphragm from striking each other when the diaphragm is in a state of vibration.

3. A device for reproducing sound including a curved diaphragm having two front meeting edges, means connected to the two front meeting edges of the diaphragm for actuating the same, and means between the two front meeting edges of the diaphragm for damping the vibrations at the said meeting edges to prevent the meeting edge portions of the diaphragm from striking each other when the diaphragm is in a state of vibration.

4. A device for reproducing sound including a flexed diaphragm having two front 7 meeting edges, means connected to the two striking each other when the front meeting edges for actuating the diaphragm and means interposed between the two front meeting edges of the diaphragm to space the same apart to prevent the meeting edge portions of the diaphragm from in a stateof vibration.

In testimony whereof I aflix my signature.

CHARLES HUGH DUFFY.

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